states. >> it was introduced into the united states in 1999, and then it spread over a series of years through the bird population. it got into the mosquitos, and then, of course, the mosquitos bit people. >> reporter: the number of cases this year is skyrocketing. nearly 1600 infections have been reported and 66 deaths, up 40% in just one week. >> it's a late summer disease, so the fact that we've got so many cases this early and it's so widespread really does not bode well. >> every state except alaska and hawaii has seen outbreaks and more than 70% of the cases come from six states. the hardest hit is texas with nearly half of the infections. health officials from coast to coast are launching efforts to prevent the spread of the potentially damage yus disease from the air, to the ground people are on patrol distributing flyers with preventative nervous and symptoms that tend to be mild. in 20% fevers, headaches and body aches and most worry some for people over 70 are with weakened immune systems. west nile virus is a known threat to animals. while there's a vaccine for horses, ther